Preprocessing apparatus for gas analysis

ABSTRACT

Provided herein is a preprocessing apparatus for gas analysis that enables preprocessing for gas analysis to be performed without requiring a cryogen. A preprocessing apparatus for gas analysis 101 mainly includes a gas flow path 103, a cooling portion 105, and a plurality of valves V101 to V105 that serve as gas flow path connection changing means for changing the gas flow path. The cooling portion 105 is operable to cool the collecting portion 113, and is constituted from a heat conductor 121, a cooling device 127, and a sealed structure 129. The cooling device 127 can cooled a contact cooling section 131 to an extremely low temperature by utilizing electrical energy. The cooling device 127 is used to bring the collecting portion 113 to a first temperature at which the target gas to be analyzed is solidified, and to thereafter bring the collecting portion 113 to a second temperature at which only the target gas to be analyzed is gasified. By performing such processes, the target gas to be analyzed can be extracted by removing gases of impurities from a mixed gas.

TECHNICAL FIELD

The present invention relates to a preprocessing apparatus for gasanalysis operable to introduce a target gas to be analyzed into a gasanalysis device.

BACKGROUND ART

Mass spectrometers and gas analysis devices such as a laser isotopespectroscopic measurement device that uses laser spectrometry have beenput into practical use. FIG. 9 is a schematic diagram illustrating anexample configuration of a preprocessing apparatus for gas analysisaccording to the related art. A preprocessing apparatus 1 for gasanalysis separates a target gas to be analyzed and gases of impuritiesfrom a mixed gas, and introduces the target gas into a gas analysisdevice. The preprocessing apparatus 1 for gas analysis mainly includes agas flow path 3, a cooling portion 5, and a plurality of valves V1 to V5that serve as gas flow path connection changing means for changing thegas flow path. The gas flow path 3 is constituted from a glass pipehaving a pipe diameter of 1 cm to 1.5 cm, and connected to a gasgenerating source 7, a vacuum pump 9, and a gas analysis device 11 viathe valves. A collecting portion 13 configured to collect the gases ofimpurities is provided in the gas flow path 3 between the valves V2 andV3. A bellows 15 and a pressure gauge 17 are provided between thecollecting portion 13 and the gas analysis device 11. The target gas isintroduced into the gas analysis device 11 at a constant pressure by thebellows 15.

The cooling portion 5 cools the collecting portion 13, and is formedfrom a Dewar vessel 19 and a cryogen put in the Dewar vessel 19.

In a conventional example, the gas generating source 7 is configuredsuch that phosphoric acid can be dropped into a container that containsa sample. Phosphoric acid is dropped onto the sample to generate a mixedgas. In this example, shells or a part of bones containing calciumcarbonate (CaCO₃) are used as the sample. When phosphoric acid isdropped onto the sample, a mixed gas containing carbon dioxide (CO₂),water (H₂O), and a minute amount of other gases is generated. CO₂ is thetarget gas to be analyzed. H₂O (and the minute amount of other gases) isthe gas of impurities. As a matter of course, the gas generating source7 may cause a reaction between a different sample and a differentsubstance. Outside air may be directly introduced to analyze a targetgas contained in the air. The vacuum pump 9 evacuates the gas flow path3 to establish a vacuum (low to middle vacuum) state.

The collecting portion 13 is formed by shaping a glass pipe into aU-shape or a spiral shape, and immersed in the cryogen put in the Dewarvessel 19 for cooling.

FIG. 10 is a flowchart according to the related art of a process inwhich the target gas to be analyzed is introduced into the gas analysisdevice 11. To introduce the target gas into the gas analysis device 11,first, the gas flow path 3 is evacuated using the vacuum pump 9, withonly the valve V5 being closed, to establish a vacuum (low to middlevacuum) state (step ST1). Then, the valves V1 and V3 are closed (stepST2), and the collecting portion 13 is immersed in a first Dewar vessel19A filled with liquid nitrogen (at about −196° C.) which serves as afirst cryogen (step ST3). When the gas generating source 7 generates agas (mixed gas) (step ST4), a pressure gradient is caused between thegas generating source 7 and the collecting portion 13 which has beencooled by the liquid nitrogen, and the generated mixed gas is collectedin the collecting portion 13 and solidified (step ST5). Specifically,CO₂ is solidified into dry ice, and H₂O is solidified into ice. Theminute amount of other gases that cannot be collected at this point isremoved utilizing the vacuum pump 9 with the valve V1 being opened (stepST6). After that, the valves V1 and V2 are closed (step ST7).

Next, the first Dewar vessel 19A is replaced with a second Dewar vessel19B filled with a second cryogen (at about −80° C.) prepared by addingethanol to liquid nitrogen (step ST8). Then, the temperature of thecollecting portion 13 is gradually raised to about −80° C., and CO₂alone is gasified with H₂O remaining ice. After that, the valve V3 isopened (step ST9) to measure the amount of generated CO₂ using thepressure gauge 17. The volume of the bellows 15 is adjusted so as toestablish a predetermined pressure (step ST10). The valves V3 and V4 areclosed, and the valve V5 is opened (step ST11). The target gas to beanalyzed is diffused or scattered to feed the target gas to the gasanalysis device (step ST12).

The foregoing is a common method of preprocessing performed before thetarget gas to be analyzed is introduced into the gas analysis device(see Non-Patent Document 1).

Recently, there has been proposed a device that also achieves thetemperature of −80° C. by heating the collecting portion 13 using aheating wire, instead of replacing the first cryogen with the secondcryogen (Non-Patent Document 2). In this device, a stainless steel pipehaving a pipe diameter of about 0.6 cm is used for gas flow path.

In the “purge and trap” method which is used for volatile gas analysis,a sample set in a thermal desorption portion is heated under an inertgas (helium), a generated gas component is adsorbed by a trap pipe(collecting portion) that has been cooled. Next, the trap pipe israpidly heated, and the adsorbed gas is introduced for gaschromatography or the like. The trap pipe (collecting portion) is cooledusing liquid nitrogen (Non-Patent Document 3).

RELATED-ART DOCUMENT Patent Documents

-   Non-Patent Document 1: “Oxygen and Hydrogen Isotope Geology (1)”, by    MATSUHISA Yukihiro, Geological News, February 1978 issue, No. 282-   Non-Patent Document 2: “Carbonate Analysis on the MultiCarb    Dual-Inlet System”, by Isoprime,    (http://www.isoprime.co.uk/files/TN010.pdf)-   Non-Patent Document 3: “Analysis of Minute Amount of Volatile    Component by P&T-GC/MS Method”, by KASAMA Atsuko and HIRANO Takeshi,    Nichias Technical Report, No. 328, June issue 2001

SUMMARY OF INVENTION Technical Problem

The biggest problem with the method described in Non-Patent Document 1is that a cryogen comprised of liquid nitrogen and a cryogen comprisedof liquid nitrogen and ethanol must be used at room temperature. This isbecause the cryogen is gradually evaporated at room temperature andneeds to be always replenished since the liquid surface in the Dewarvessel becomes lower if the cryogen is left as it is. According to ameasurement by the inventor, as illustrated in FIG. 11, the temperatureof the cryogen in the Dewar vessel (having a height of 22 cm and adiameter of 8.5 cm) tends to be higher at lower portions and on theouter side than at upper portions and on the inner side, respectively.Thus, it is difficult to keep the temperature of the liquid nitrogenconstant. In addition, it is necessary to immerse the collecting portion13 in the cryogen in the Dewar vessel 19, and therefore it is necessaryto shape the collecting portion 13 so as to extend downward. Thecollecting portion 13 must have some degree of size since a glass pipeis used for the collecting portion 13. Further, in some cases, aconcentration step is necessary to concentrate the target gas to beanalyzed before the target gas is fed to the gas analysis device sincethe space in the glass pipe is large for the amount of the target gas tobe analyzed, which makes the target gas thinner. Also in theconcentration step, it is necessary to use liquid nitrogen as thecryogen. Further, when the Dewar vessel 19A is replaced with the Dewarvessel 19B, the glass pipe is exposed to room temperature, although onlyfor a short time. Therefore, there is a risk that the mixed gas whichhas been solidified may be gasified, and quick replacement is required.

The device described in Non-Patent Document 2 does not requirereplacement of Dewar vessels. However, the device also uses liquidnitrogen as a cryogen, and therefore has the same issues as those ofNon-Patent Document 1.

An object of the present invention is to provide a preprocessingapparatus for gas analysis that enables preprocessing for gas analysisto be performed without requiring a cryogen.

Another object of the present invention is to provide a preprocessingapparatus for gas analysis that obtains a target gas to be analyzed thathas a sufficient concentration even without performing a step ofconcentrating the target gas to be analyzed.

Solution to Problem

A preprocessing apparatus for gas analysis according to the presentinvention includes, as basic components, a gas flow path including acollecting portion that is cooled in order to collect a target gas to beanalyzed, and a cooling device operable to cool the collecting portionof the gas flow path. Further, a preprocessing apparatus for gasanalysis, which separates the target gas from a mixed gas, includes: agas flow path including a collecting portion that is cooled to aplurality of temperature levels in order to separate a target gas to beanalyzed and gases of impurities from a mixed gas containing a pluralityof kinds of gases; a cooling device operable to cool the collectingportion of the gas flow path to the plurality of temperature levels; anda gas flow path connection changing means for connecting the gas flowpath to a vacuum pump when evacuating the gas flow path, connecting thegas flow path to a gas generating source when introducing the mixed gasinto the gas flow path after the gas flow path has been evacuated, andconnecting the gas flow path to a gas analysis device in order to supplythe target gas, which has been separated by the collecting portion, tothe gas analysis device. The collecting portion is cooled to a pluralityof temperature levels according to the solidification temperature of thetarget gas. In general, the collecting portion is often cooled to aplurality of temperature levels in order to separate a gas having thelowest solidification temperature, as a target gas to be analyzed, froma mixed gas containing a plurality of kinds of gases and to collectother kinds of gases other than the target gas, as gases of impurities.

The preprocessing apparatus for gas analysis according to the presentinvention further includes a heat conductor configured to surround anouter periphery of the collecting portion. The cooling device includes acontact cooling section configured to contact the collecting portion touniformly cool the collecting portion to a set temperature, and has atemperature adjusting function of adjusting a temperature of the contactcooling section to an arbitrary temperature by utilizing electricalenergy. By using such a cooling device, it is possible to uniformly coolthe entire collecting portion without using a cryogen such as liquidnitrogen, and to easily introduce the target gas to be analyzed into thegas analysis device. Since there is no need to use a cryogen, thedirection of extension of the collecting portion is not limited, and itis not necessary to shape the collecting portion so as to extenddownward as in the related art. The cooling device is specifically astirling cooler.

In order to efficiently cool the collecting portion, the collectingportion, the heat conductor, and the contact cooling section may bereceived in a vacuum chamber of a sealed structure, the vacuum chamberbeing connected to a vacuum pump and evacuated; and the vacuum chambermay have been brought into a vacuum state by the vacuum pump when thecollecting portion is cooled. With such a configuration, the collectingportion can be cooled without being affected by air or room temperature.In addition, if the heat conductor contacts the contact cooling sectionvia an indium sheet, the collecting portion can be cooled moreefficiently.

In order to stabilize the mixed gas which passes inside the collectingportion, the collecting portion is preferably meanderingly arranged inthe heat conductor. Further, if the collecting portion is meanderinglyarranged along a cooling surface of the contact cooling section, alarger portion of the collecting portion can be cooled by the contactcooling section, thereby efficiently cooling the collecting portion.Most suitably, the collecting portion has an overall length of 5 cm ormore and 15 cm or less. The preprocessing apparatus for gas analysisaccording to the present invention does not need to use liquid nitrogen,and therefore does not need to use a glass pipe. Therefore, thecollecting portion can have a diameter of one-eighth of an inch (3.175mm) or less, and further one-sixteenth of an inch (1.5875 mm) or less.

If the collecting portion is a gas pipe, the heat conductor ispreferably insert molded including the gas pipe as an insert. With sucha configuration, the gas pipe and the heat conductor are unitarilyformed, which enables the gas pipe as the collecting portion to beefficiently cooled.

The heat conductor may include a heater configured to be electricallyenergized to generate heat. With such a heater, the collecting portionwhich has been cooled by the cooling device can be heated, which enablesquick temperature adjustment.

The preprocessing apparatus for gas analysis according to the presentinvention is used to introduce a target gas to be analyzed into a gasanalysis device. For example, the preprocessing apparatus for gasanalysis can be used to remove water (H₂O) as an impurity from a mixedgas generated by adding phosphoric acid to a sample and introducingcarbon dioxide (CO₂) as a target gas into a gas analysis device. As amatter of course, however, the present invention is not limited thereto.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating an example configuration of apreprocessing apparatus for gas analysis according to an embodiment ofthe present invention.

FIGS. 2A and 2B are a plan view and a front view, respectively,illustrating a collecting portion and a heat conductor with the heatconductor being rendered transparent.

FIG. 3 is a front view illustrating the configuration of a coolingportion operable to cool the collecting portion.

FIG. 4 is a plan view illustrating a contact cooling section of acooling device.

FIGS. 5A, 5B, and 5C are a plan view, a front view, and a sectional viewtaken along line C-C, respectively, of a lower structure forming asealed structure.

FIGS. 6A, 6B, and 6C are a plan view, a front view, and a sectional viewtaken along line C-C, respectively, of an upper structure forming thesealed structure.

FIG. 7 illustrates an example heat conductor including a heater, whereinFIGS. 7A and 7B are a plan view and a front view, respectively,illustrating the collecting portion, the heat conductor, and the heaterwith the heater and the heat conductor being rendered transparent.

FIG. 8 is a flowchart according to the embodiment of a process until atarget gas to be analyzed is introduced into a gas analysis device.

FIG. 9 is a schematic diagram illustrating the configuration of aconventional preprocessing apparatus for gas analysis.

FIG. 10 is a flowchart of a conventional process until a target gas tobe analyzed is introduced into a gas analysis device.

FIG. 11 illustrates the temperature distribution of liquid nitrogen in aDewar vessel.

DESCRIPTION OF EMBODIMENTS

A preprocessing apparatus for gas analysis according to an embodiment ofthe present invention will be described in detail below with referenceto the accompanying drawings.

FIG. 1 is a schematic diagram illustrating the configuration of apreprocessing apparatus for gas analysis according to an embodiment.FIGS. 2A and 2B are a plan view and a front view, respectively,illustrating a collecting portion and a heat conductor with the heatconductor being rendered transparent. FIG. 3 is a front viewillustrating the configuration of a cooling portion. FIG. 4 is a planview illustrating a contact cooling section of a cooling device. FIGS.5A, 5B, and 5C are a plan view, a front view, and a sectional view takenalong line C-C, respectively, of a lower structure forming a sealedstructure. FIGS. 6A, 6B, and 6C are a plan view, a front view, and asectional view taken along line C-C, respectively, of an upper structureforming the sealed structure.

As with the conventional preprocessing apparatuses for gas analysis, apreprocessing apparatus 101 for gas analysis mainly includes a gas flowpath 103, a cooling portion 105, and a plurality of valves V101 to V105that serve as gas flow path connection changing means for changing thegas flow path. The preprocessing apparatus 101 for gas analysis isdifferent from the conventional preprocessing apparatus for gas analysismainly in the configuration of a collecting portion 113 and the coolingportion 105 which cools the collecting portion 113. The preprocessingapparatus for gas analysis of the embodiment will be described below,focusing on the differences from the conventional preprocessingapparatuses for gas analysis. Common members are denoted by referencenumerals obtained by adding 100 to the reference numerals affixed totheir counterparts of the conventional preprocessing apparatus for gasanalysis illustrated in FIG. 9, and explanations of such parts areoccasionally omitted.

The gas flow path 103 of the embodiment is formed from a stainless steelalloy pipe having a pipe diameter of one-sixteenth of an inch (1.5875mm) to one-eighth of an inch (3.175 mm), and connected to a gasgenerating source 107, a vacuum pump 109, and a gas analysis device 111via valves. The gas flow path 103 includes a collecting portion 113provided between the valves V102 and V103 and configured to collectgases of impurities. A bellows 115 and a pressure gauge 117 are providedbetween the collecting portion 113 and the gas analysis device 111. Thetarget gas to be analyzed is introduced into the gas analysis device 111at a constant pressure by the bellows 115.

[Collecting Portion and Heat Conductor]

The collecting portion 113 of the embodiment is a gas pipe made of astainless steel alloy illustrated in FIG. 2. As the collecting portion,a pas pipe suitably has an overall length of 5 cm to 15 cm and adiameter of one-sixty-fourth of an inch (0.396875 mm) to one-eighth ofan inch (3.175 mm). Use of such thin pipe having a small diameter canomit a step of concentrating the target gas to be analyzed, which isperformed in the conventional method that uses a glass pipe having alarge internal space. In gas chromatography, for example, whichintroduces a target gas into an analysis device using a carrier gas suchas helium gas, a thin pipe having a small diameter, for example, ofone-sixty-fourth of an inch (0.396875 mm) to one-sixteenth of an inch(1.5875 mm) is generally used for effective introduction or feeding ofthe target gas as with the embodiment of the present invention. Thepresent invention can be directly applied to such devices. In theembodiment, the gas pipe has an overall length of 12 cm and a diameterof one-sixteenth of an inch (1.5875 mm). The outer periphery of thecollecting portion 113 is surrounded by a heat conductor 121 made of astainless steel alloy. The collecting portion 113 is meanderinglyarranged in the heat conductor 121. In the embodiment, the heatconductor 121 is insert molded including the gas pipe, which is thecollecting portion 113, as an insert. The heat conductor 121 has atemperature sensor insertion hole 123 formed therein for insertion of atemperature sensor configured to measure the temperature of thecollecting portion 113. The heat conductor 121 also has through holes125, 125 formed therein for fixation of the heat conductor 121 to acooling device that will be discussed later. The dimensions of therespective portions are as illustrated in FIG. 2.

[Cooling Portion]

The cooling portion 105 is operable to cool the collecting portion 113,and is constituted from the heat conductor 121, a cooling device 127,and a sealed structure 129 as illustrated in FIG. 3. In FIG. 3, a lowerstructure 139 and an upper structure 141 of the sealed structure 129 areillustrated in section.

The cooling device 127 includes a disc-shaped contact cooling section131 configured to contact the heat conductor 121 to uniformly cool thecollecting portion 113 to a set temperature, and has a temperatureadjusting function of adjusting the temperature of the contact coolingsection 131 to an arbitrary temperature by utilizing electrical energy.In the embodiment, the cooling device 127 is specifically a stirlingcooler operable to achieve an extremely low temperature through stirlingcycles including constant-volume heating, isothermal expansion,constant-volume cooling, and isothermal compression. In the embodiment,more specifically, a “Cryo Cooler (model name: SC-UF01)” manufactured byTwinbird Corporation is used as the cooling device 127. SC-UF01 canbring the contact cooling section 131 to an extremely low temperature ora cryogenic temperature lower than −200° C. by utilizing electricalenergy, and can finely control the temperature in units of 0.1° C. Asillustrated in FIG. 4, four screw holes 133 are formed in a coolingsurface 131A of the contact cooling section 131. The heat conductor 121is fixed to the contact cooling section 131 by screws 135. In order toenhance the heat conduction efficiency, an indium sheet 137 isinterposed between the heat conductor 121 and the contact coolingsection 131.

As illustrated in FIGS. 2 to 4, the collecting portion 113 ismeanderingly arranged along the cooling surface 131A of the contactcooling section 131. With such arrangement of the collecting portion113, a larger portion of the collecting portion 113 can be cooled by thecontact cooling section 131, and the gas which passes inside thecollecting portion 113 can be stabilized. The attitude of installationof SC-UF01 is not limited to that illustrated in FIG. 3, and SC-UF01 maybe installed in a laid state. Another advantage of using SC-UF01 and thecollecting portion 113 is that SC-UF01 can be in an attitude thatmatches the location of installation. This is a difference from theconventional preprocessing method which uses a cryogen.

The sealed structure 129 is intended to receive the collecting portion113, the heat conductor 121, and the contact cooling section 131 of thecooling device 127. The contact cooling section 131 is received insidethe sealed structure 129 such that a clearance of about 10 mm isprovided between the outer periphery of the contact cooling section 131and the sealed structure 129 and a clearance of about 10 mm is providedbetween the upper and lower surfaces of the contact cooling section 131and the sealed structure 129 in the vertical direction. The spacedefined by such clearances allows evacuation to be completed in a shorttime, and enables appropriate heat insulation.

As illustrated in FIG. 3, the sealed structure 129 is constituted fromtwo members, namely the lower structure 139 and the upper structure 141.As illustrated in FIGS. 5A to 5C, the lower structure 139 has acylindrical shape, and is provided with a flange 139A to be fixed to thecooling device 127 at one end portion and a flange 139B to be fixed tothe upper structure 141 at the other end portion. The flange 139B isprovided with two groove portions 143A and 143B configured to receive apart of a pipe that connects to the gas pipe (see FIG. 2) made ofstainless steel and forming the collecting portion 113. The flange 139Bhas four screw holes 145 formed therein for fixation of the upperstructure 141.

As illustrated in FIGS. 6A to 6C, the upper structure 141 is a lid-likemember having an opening at one end portion and a bottom at the otherend portion and configured to block the other end portion of the lowerstructure 139. A flange 141A to be fixed to the flange 139B of the lowerstructure 139 is provided at the opening end portion of the upperstructure 141. The flange 141A has screw holes 147 formed therein atpositions corresponding to the screw holes 145. A bottom portion 141B ofthe upper structure 141 has a vacuum pump connection hole 149 formedtherein for connection to the vacuum pump when evacuating the sealedstructure 129.

To constitute a vacuum chamber, a flange portion 128 (FIG. 3) of thecooling device 127 and the flange 139A of the lower structure 139 arefixed to each other by a vacuum clamp (not illustrated) with an O-ringinterposed therebetween, and the flange portion 139B of the lowerstructure 139 and the flange 141A of the upper structure 141 are fixedto each other by screws (not illustrated) with an O-ring interposedtherebetween. Thus, the sealed structure 129 is obtained. The sealedstructure 129 is evacuated using a vacuum pump. With this configuration,the collecting portion 113, the heat conductor 121, and the contactcooling section 131 of the cooling device 127 are thermally insulatedfrom the outside, which enables the collecting portion 113 to beefficiently cooled.

FIGS. 7A and 7B illustrate an example configuration in which the heatconductor 121 is provided with a heater 122. A cable connected to apower source etc. is not illustrated. In FIG. 7A, only the outline ofthe heater 122 is schematically indicated by broken lines. The heater122 is a sheet-like heater, and is configured to be electricallyenergized to generate heat. The heater 122 is provided on a surface ofthe heat conductor 121 opposite to the surface which contacts thecontact cooling section 131. It is optional whether or not to providethe heater 122. The heater 122 is useful if it is desirable to quicklyraise the temperature of the collecting portion.

[Gas Generating Source]

In the embodiment, the gas generating source 107 is configured such thatphosphoric acid can be dropped into a container that contains a sample.Phosphoric acid is dropped onto the sample to generate a mixed gas. Inthis embodiment, shells or a part of bones containing calcium carbonate(CaCO₃) are used as the sample. When phosphoric acid is dropped onto thesample, a mixed gas containing carbon dioxide (CO₂), water (H₂O), and aminute amount of other gases is generated. CO₂ is the target gas to beanalyzed. H₂O (and the minute amount of other gases) is the gas ofimpurities.

[Flowchart of Process Until Target Gas to be Analyzed is Introduced intoGas Analysis Device]

FIG. 8 is a flowchart of a process until the target gas to be analyzedis introduced into the gas analysis device 111. To introduce the targetgas into the gas analysis device 111, first, the gas flow path 103 isevacuated using the vacuum pump 109, with only the valve V105 beingclosed, to establish a vacuum (low to middle vacuum) state. In addition,the sealed structure 129 is evacuated to establish a vacuum (low tomiddle vacuum) state (step ST1). Then, the valves V101 and V103 areclosed (step ST2), and the collecting portion 113 is brought to a firsttemperature using the cooling device 127 (step ST3). The firsttemperature may be a temperature at which CO₂ as the target gas issolidified (a temperature lower than the sublimation point). In theembodiment, CO₂ is cooled to −196° C. as in the conventionalpreprocessing method. In this embodiment, the gas flow path 103 has beenevacuated to about 0 to 5 Torr (1.013 bar to 1.019 bar), and thereforethe sublimation point is slightly lower than −78.5° C. that is thesublimation point at normal pressure.

When the gas generating source 107 generates a gas (mixed gas) (stepST4), a pressure gradient is caused between the gas generating source107 and the collecting portion 113 which has been cooled, and thegenerated mixed gas is collected in the collecting portion 113 andsolidified (step ST5). Specifically, CO₂ is solidified into dry ice, andH₂O is solidified into ice. The minute amount of other gases that cannotbe collected at this point is removed utilizing the vacuum pump 109 withthe valve V101 being opened (step ST6). After that, the valves V101 andV102 are closed (step ST7).

Next, the collecting portion 113 is brought to a second temperatureusing the cooling device 127. The second temperature may be atemperature around or higher than the temperature at which CO₂ isgasified (sublimation point). In the embodiment, the temperature israised to −80° C. as in the conventional preprocessing method. If theheater 122 is provided, the heater 122 is actuated to quickly raise andadjust the temperature. To measure a sample containing much water, it ispreferable to set the temperature to be low in order to remove as muchwater (H₂O) as possible. Therefore, it is desirable to adjust the secondtemperature according to the state of the sample or the like. When thetemperature of the collecting portion 113 is raised to the secondtemperature, CO₂ alone is gasified with H₂O remaining in an ice state.After that, the valve V103 is opened (step ST9) to measure the amount ofgenerated CO₂ using the pressure gauge 117. The volume of the bellows115 is adjusted so as to achieve a predetermined pressure (step ST10).The valves V103 and V104 are closed and the valve V105 is opened (stepST11). The target gas to be analyzed is diffused to feed the target gasto the gas analysis device 111 (step ST12).

In the embodiment, it is not necessary to use liquid nitrogen.Therefore, it is not necessary to use a glass pipe or a stainless steelpipe having a large diameter, and the collecting portion 113, inparticular, can be formed from a gas pipe that is made of a stainlesssteel alloy and that is thin and short compared to the conventionalglass pipe as discussed above. Therefore, the space in the collectingportion 113 is small, which makes it possible to make the target gasthick compared to the related art. The target gas having a sufficientconcentration can be obtained even if the step of concentrating thetarget gas is not performed before the target gas is fed to the gasanalysis device. As a matter of course, this does not mean to excludethe concentration step, and the concentration step may be performeddepending on the analysis content or the like.

While an exemplary embodiment of the present invention has beenspecifically described above, the present invention is not limited tosuch an embodiment, and it is a matter of course that changes,modifications, or variations may be made within the scope of thetechnical concept of the present invention. For example, the presentinvention can also be used when an organic matter is used as a sample, asilica glass pipe containing the organic matter is evacuated and thensealed to prepare a sealed pipe, the sealed pipe is burnt to generate amixed gas containing CO₂, water, NO_(R), and SO_(x), and NO_(x) andSO_(x) containing water as gases of impurities are removed. This methodis used in a radiocarbon isotope dating method that is widely used inarcheology and geology. In this method, it is necessary to preparehigh-purity CO₂ from which impurities have been completely removed, andto prepare graphite from the high-purity CO₂. In this case, the firsttemperature and the second temperature for the cooling device 127 may beset to −196° C. and −130° C., respectively, since NO_(x) and SO_(x) canbe trapped when cooled to −130° C.

The target gas to be analyzed and the gases of impurities are separatedfrom each other utilizing the solidification temperatures of therespective gases and the temperatures at which the gases are gasifiedfrom a solid state. Therefore, even if one of the gases of impuritieshas the lowest solidification temperature or a plurality of gases ofimpurities are mixed, the target gas can be extracted by settingcorresponding temperature levels. For example, the target gas is CO₂ inthe above embodiment. If the target gas is water, the collecting portioncan be cooled stepwisely to a plurality of temperature levels. Forexample, the mixed gas is cooled to a first temperature at which CO₂ canbe solidified, thereafter CO₂ is gasified at a second temperature higherthan the first temperature, then CO₂ is discharged using a pump, andthereafter the temperature is raised to a third temperature of 0° C. orhigher to obtain only water.

The present invention is also applicable to implement the “purge andtrap” method which is used in volatile gas analysis. In the “purge andtrap” method, a sample set in a thermal desorption portion is heatedunder an inert gas (helium), and a generated gas component is adsorbedby a trap pipe (collecting portion) that has been cooled. Next, the trappipe is rapidly heated, and the adsorbed gas is introduced into a gaschromatograph for gas chromatography or the like. The trap pipe(collecting portion) may be cooled and heated using a device that issimilar to the preprocessing apparatus for gas analysis according to theembodiment described above.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to performpreprocessing for gas analysis, in which a target gas to be analyzed isextracted, without using a cryogen. In addition, a target gas to beanalyzed that has a sufficient concentration can be obtained evenwithout performing a step of concentrating the target gas to beanalyzed.

DESCRIPTION OF REFERENCE NUMERALS

-   101 preprocessing apparatus for gas analysis-   103 gas flow path-   105 cooling portion-   107 gas generating source-   109 vacuum pump-   111 gas analysis device-   113 collecting portion-   115 bellows-   117 pressure gauge-   121 heat conductor-   123 temperature sensor insertion hole-   125 through hole-   127 cooling device-   129 sealed structure-   131 contact cooling section-   133 screw hole-   135 screw-   137 indium sheet-   139 lower structure-   141 upper structure-   143 groove portion-   145 through hole-   147 through hole-   149 vacuum pump connection hole

The invention claimed is:
 1. A preprocessing apparatus for gas analysiscomprising: a gas flow path including a collecting portion that iscooled to a plurality of temperature levels in order to separate a gashaving the lowest solidification temperature, as a target gas to beanalyzed, from a mixed gas containing a plurality of kinds of gases andto collect other kinds of gases other than the target gas, as gases ofimpurities; a cooling device operable to cool the collecting portion ofthe gas flow path to the plurality of temperature levels; a gas flowpath connection changing means for connecting the gas flow path to avacuum pump when evacuating the gas flow path, connecting the gas flowpath to a gas generating source when introducing the mixed gas into thegas flow path after the gas flow path has been evacuated, and connectingthe gas flow path to a gas analysis device in order to supply the targetgas to be analyzed, which has been separated by the collecting portion,to the gas analysis device; and a heat conductor configured to surroundan outer periphery of the collecting portion, wherein the cooling deviceincludes a contact cooling section configured to contact the heatconductor to uniformly cool the collecting portion to a set temperature,and has a temperature adjusting function of adjusting a temperature ofthe contact cooling section to an arbitrary temperature by utilizingelectrical energy; the collecting portion, the heat conductor, and thecontact cooling section are received in a vacuum chamber of a sealedstructure, the vacuum chamber being connected to a vacuum pump andevacuated; and, the vacuum chamber has been brought into a vacuum stateby the vacuum pump when the collecting portion is cooled.
 2. Thepreprocessing apparatus for gas analysis according to claim 1, whereinthe heat conductor contacts the contact cooling section via an indiumsheet.
 3. The preprocessing apparatus for gas analysis according toclaim 2, wherein the collecting portion is meanderingly arranged along acooling surface of the contact cooling section.
 4. The preprocessingapparatus for gas analysis according to claim 2, wherein the collectingportion has an overall length of 5 cm or more and 15 cm or less.
 5. Thepreprocessing apparatus for gas analysis according to claim 2, whereinthe collecting portion has a diameter of one-eighth of an inch (3.175mm) or less.
 6. The preprocessing apparatus for gas analysis accordingto claim 1, wherein the collecting portion is meanderingly arranged inthe heat conductor.
 7. The preprocessing apparatus for gas analysisaccording to claim 1, wherein: the collecting portion is a gas pipethrough which the mixed gas flows; and the heat conductor is insertmolded including the gas pipe as an insert.
 8. The preprocessingapparatus for gas analysis according to claim 1, wherein the heatconductor includes a heater configured to be electrically energized togenerate heat.
 9. The preprocessing apparatus for gas analysis accordingto claim 1, wherein: the mixed gas is a gas generated by addingphosphoric acid to a sample; a main component of the impurities iswater; and the target gas to be analyzed is carbon dioxide.
 10. Apreprocessing apparatus for gas analysis comprising: a gas flow pathincluding a collecting portion that is cooled to a plurality oftemperature levels in order to separate a plurality of kinds of gasescontained in a mixed gas into a target gas to be analyzed and gases ofimpurities; a cooling device operable to cool the collecting portion ofthe gas flow path to the plurality of temperature levels; a gas flowpath connection changing means for connecting the gas flow path to avacuum pump when evacuating the gas flow path, connecting the gas flowpath to a gas generating source when introducing the mixed gas into thegas flow path after the gas flow path has been evacuated, and connectingthe gas flow path to a gas analysis device in order to supply the targetgas to be analyzed, which has been separated by the collecting portion,to the gas analysis device; and a heat conductor configured to surroundan outer periphery of the collecting portion, wherein the cooling deviceincludes a contact cooling section configured to contact the heatconductor to uniformly cool the collecting portion to a set temperature,and has a temperature adjusting function of adjusting a temperature ofthe contact cooling section to an arbitrary temperature by utilizingelectrical energy; the collecting portion, the heat conductor, and thecontact cooling section are received in a vacuum chamber of a sealedstructure, the vacuum chamber being connected to a vacuum pump andevacuated; and, the vacuum chamber has been brought into a vacuum stateby the vacuum pump when the collecting portion is cooled.
 11. Thepreprocessing apparatus for gas analysis according to claim 10, wherein:the collecting portion, the heat conductor, and the contact coolingsection are received in a vacuum chamber of a sealed structure, thevacuum chamber being connected to a vacuum pump and evacuated; and thevacuum chamber has been brought into a vacuum state by the vacuum pumpwhen the collecting portion is cooled.
 12. The preprocessing apparatusfor gas analysis according to claim 10, wherein the heat conductorcontacts the contact cooling section via an indium sheet.
 13. Thepreprocessing apparatus for gas analysis according to claim 10, whereinthe collecting portion is meanderingly arranged in the heat conductor.14. The preprocessing apparatus for gas analysis according to claim 10,wherein: the collecting portion is a gas pipe through which the mixedgas flows; and the heat conductor is insert molded including the gaspipe as an insert.
 15. A preprocessing apparatus for gas analysiscomprising: a gas flow path including a collecting portion that iscooled in order to collect a target gas to be analyzed; a cooling deviceoperable to cool the collecting portion of the gas flow path; and a heatconductor configured to surround an outer periphery of the collectingportion, wherein the cooling device includes a contact cooling sectionconfigured to contact the heat conductor to uniformly cool thecollecting portion to a set temperature, and has a temperature adjustingfunction of adjusting a temperature of the contact cooling section to anarbitrary temperature by utilizing electrical energy; the collectingportion, the heat conductor, and the contact cooling section arereceived in a vacuum chamber of a sealed structure, the vacuum chamberbeing connected to a vacuum pump and evacuated; and, the vacuum chamberhas been brought into a vacuum state by the vacuum pump when thecollecting portion is cooled.
 16. The preprocessing apparatus for gasanalysis according to claim 15, wherein: the collecting portion, theheat conductor, and the contact cooling section are received in a vacuumchamber of a sealed structure, the vacuum chamber being connected to avacuum pump and evacuated; and the vacuum chamber has been brought intoa vacuum state by the vacuum pump when the collecting portion is cooled.17. The preprocessing apparatus for gas analysis according to claim 15,wherein the heat conductor contacts the contact cooling section via anindium sheet.
 18. The preprocessing apparatus for gas analysis accordingto claim 15, wherein the collecting portion is meanderingly arranged inthe heat conductor.
 19. The preprocessing apparatus for gas analysisaccording to claim 15, wherein: the collecting portion is a gas pipethrough which the mixed gas flows; and the heat conductor is insertmolded including the gas pipe as an insert.